The present invention relates to a method and apparatus for controlling an ink supply amount for a printing press.
As a conventional method of controlling an ink supply amount of this type, image areas of a plurality of zones obtained by dividing a plate surface are measured, and the image areas of each zone of the plate surface are averaged to obtain an average image area. A rotational speed Ts of an ink fountain roller is determined in accordance with the resultant average image area, and opening degrees S.sub.01 to S.sub.0n of ink fountain keys of the respective zones are obtained on the basis of the image areas of the respective zones. An ink supply amount is controlled on the basis of the resultant rotational speed Ts and the opening degrees S.sub.01 to S.sub.0n as initial values.
In the conventional method of controlling an ink supply amount described above, the rotational speed Ts of the ink fountain roller or the like is changed to adjust (color registration) an ink density so as to match a rotational frequency (printing speed) V.sub.x for the printing press. However, it is difficult to maintain a predetermined density according to this method because the rotational speed Ts of the ink fountain roller increases with an increase in printing speed V.sub.x.
This may be caused by various factors such as expansion of the ink fountain roller by ink stirring heat and a decrease in contact area of an ink feed roller by a jump during damping. In addition to these factors, at a portion where the opening degree of the ink fountain key is small, a flow resistance increases at a gap between the ink fountain key and the ink fountain roller with an increase in rotational speed Ts of the ink fountain roller. It is difficult to properly supply an ink at this portion. As a result, in a rotary printing press, when the rotational speed Ts of the ink fountain roller increases, the ink density is excessively increased at a portion where the opening degree of the ink fountain key is large. To the contrary, the ink density is excessively decreased at a portion where the opening degree of the ink fountain key is small, resulting in inconvenience.
When the rotational speed Ts of the ink fountain roller is changed to adjust the ink density, a color registration time is undesirably prolonged, and the number of waste paper sheets disadvantageously increases. When the movement of the ink feed roller and the speed of the ink fountain roller increase, the durability of mechanical components is degraded, and electrical components are overloaded.